With adjustable pulleys you can gt very good results if you know what are you doing, especially in the mid range, that is where the turbo starts to make boost, thus reducing turbo lag. You don't have to use them, but if you do it set them up well you can get very good results.
The only problem is that to do it well you have to know about it, or leave it to somebody that knows what he is doing. In this engine is even worse because you have to undo the rocker cover to make adjustments, so it makes it harder to set up because the camshafts are chain driven, so you would have to think if is worth the hassle.